1. Field of the Invention
The present invention relates to a clamp apparatus, which is capable of retaining a workpiece by a clamp arm through a drive force of a driving section.
2. Description of the Related Art
Heretofore, for example, when structural components of an automobile or the like are welded, a clamp apparatus is used for clamping the structural components.
In this type of clamp apparatus, for example, a piston is displaced under the supply of air, thereby causing rotary movement of a clamp arm through the piston for clamping the workpiece. However, in a state in which the workpiece is clamped, in the event that the supply of air is halted for some reason, the clamped state of the clamp arm with respect to the workpiece becomes released and the held state of the workpiece cannot be maintained, thus resulting in the workpiece being dropped from the clamp apparatus or the like.
In response to the aforementioned problems, for example, a clamp apparatus is known, which is equipped with a locking mechanism capable of regulating the rotary movement of a clamp arm. As disclosed in Japanese Laid-Open Patent Publication No. 2005-061526, in such a clamp apparatus, a lock rod is connected to a piston that slides in a cylinder body and is displaced integrally with the piston, while in addition, the clamp arm is disposed rotatably through a toggle mechanism on a piston rod connected to the piston, whereby the clamp arm is operated to open and close by displacement of the piston.
Further, a locking cylinder is disposed displaceably in a head cover of the cylinder body, the locking cylinder being disposed perpendicular to the axis of the cylinder body, with a locking piston disposed for displacement in the interior thereof. In addition, the locking piston is urged toward the side of a lock rod by a locking spring, such that by insertion of the locking piston into a recess of the lock rod, displacement of the lock rod is regulated along with regulating the rotary movement of the clamp arm.
However, in the aforementioned conventional technique, the clamp arm is stopped by insertion of the locking piston into the recess of the lock rod, which is urged by means of the locking spring. As a result, the clamping force applied to the workpiece tends to be small. In addition, in the case that a variance occurs in the thickness of the workpiece, the clamped state becomes unstable, and there is a fear that the workpiece may be subjected to shifting and cannot be positioned at a desired position.
Further, because the locking cylinder, including the locking spring and the locking piston, must be assembled in the clamp apparatus, the structure of the clamp apparatus is complicated and made larger in scale.